Free-piston compressor



1950 a. MERCIER ETAL 2,493,355

FREE-PISTON COMPRESSOR Filed lay 29, 1945 3 Sheets-Sheet 1 21 &

Ernest Merc'm' and Marczlfhlin er mv: NTQR Jan- 3, 1950 E. MERCIER EI'AL 2,493,355

FREE-PISTON COIPRBSSOR Filed llay 29, 1945 3 Sheets-Sheet 2 Fig.3

EH15? Mdfcitr and MarcglEhh'nqer INVENTORS m 1950 E. MERCIER ETAL 2,

PRES-PISTON COMPRESSOR Filed lay 29, 1945 3 Sheets-Sheet 3 Fig.4.

firm stMzrciu anql "mama;

Their Attomtq Patonted Jan. 3, 1950 FREE-PISTON oomsssoa Ernest Mercier and Marcel Ellllngu,

, by mane asdgmnents, to

Paris.

allignors Moore, Inc., Atlanta, 6a., a corporation of Georgia Application M81 29, 1.45. Serial No. no

In France October 2. 1942 m Section 1, Public Pa t Law 890, AugustB, 1946 berl, 1962 ten expiresooto 18 Claims. 1

Various types of tree-piston machines are known, some of which belong to the compressor and the others to the generator class. In such machines the driving elements usually are twinpiston internal combustion cylinders and may be of the Diesel type, which are variously arranged. The internal combustion motor or engine lends itself particularly well to that kind of application, especially as it alone allows the construction of machines of the generator type. However, an account of the rupturing force of the explosions and other disturbances in the motors of this type, heavy and intricate safety attachments must be provided to preclude accidents which may be caused by too long a travel of the free pistons. Moreover, up to the present, such machines can be run only on liquid fuels.

This invention allows the construction of freepiston machines of the compressor type which possess characteristics that are wholly comparable to those of free-piston machines having internal combustion prime movers, especially as far as the linear speed of the movable members, the number of strokes, etc., are concerned. but without resorting to combustion or explosion motors as their prime movers.

In the machines covered by this invention, the driving elements comprise one or several twinpiston cylinders in which the working iluid is either steam or compressed air or any compressed gas in which no combustive reaction takes place within the cylinder. The invention is not concerned with machines such as the conventional locomotive feed-pumps, which possess none of the characteristics of the free-piston machines and which particularly involve the use of no appreciable kinetic energy.

This invention relates particularly to direct action compressors the movable systems of which, towards the middle of their strokes, possess a considerable kinetic energy. It therefore relates to a new class of machines designed for the production at low cost of compressed air or gases, said machines having free pistons, i. e. being free from rod-and-crank mechanical transmission systems, and being composed of aircompressing cylinders in any suitable number and arrangement, which are driven directly by twin-piston steam or compressed-air motors into which the working fluid is fed with partial admission, the energy therein being transformed first into kinetic energy in the movable systems by which said energy is then transferred to the fluid to be compressed.

contrary to the Diesel motors or the freepiston machines known up to the present, in which the distribution of the iluid is controlled by the working pistons which alternately open and close ports at the ends of the cylinders, and free-piston steam engines of the invention are provided with intake ports located in the middle portion of the cylinders. and said ports are provided with cut-oi! members actuated as desired depending on the load and the characteristics of the working fluid.

Such control involves some difliculties in reciprocating machines, but such difliculties can be overcome in many ways, particularly by compressed air or steam control of the cut-off members of the kind providing the subject matter of the French patent application filed on the 12th of September 1942 for Improvements to freepiston generators, by the applicants.

The said difliculty can also be solved, according to this inventio by converting the rocking motion into a continuous rotary motion. For that purpose, the rocking shaft is fitted with a crank-and-rod system which yieldingly actuates a rotary shaft which drives the attachments, that is, the fluid distribution gear or mechanism and which is endowed with a definite inertia. First, the angle swept is converted into an angle of about the shaft which is rocked through that angle then being coupled with the rod. A uniform movement can be imparted to the shaft which drives the attachments by the interposition of a friction and/or a spring coupling sleeve.

In a free-piston steam engine the successive operations are the following:

Assumin the driving pistons are at their central dead centres, the exhaust ports must be closed and the inlet ports open. By the action of steam pressure the pistons move apart, carrying the compressing pistons in their movements according to the usual method. During said movement the intake ports are fully open until a time pro-determined in relation with the desired operation of the machine. Exactly at that time the intake ports are closed again. The steam present in the cylinder expands and the pistons continue to move up to the end of their strokes.

At the end of the stroke or slightly before (exhaust'lead) the exhaust ports are opened either by cut-off members or by the pistons themselves, according to the so-called uniflow system, and during the return stroke the steam present in the cylinder is expelled by the movemeat of the pistons. Said exhaust ports thus quently used on free-piston machines equipped with internal combustion motors.

Safety in operation may be obtained in the machines of the invention, for instance by closing the compressor delivery valves at the end of the stroke in order to provide a resisting cushion in the event that a long stroke takes place. The danger of too long strokes is decreased to a considerable extent since steam engines are obviously free from the rupturing force oi explosions and like disturbances encountered in combustion or explosion motors.

The application of this invention to free-piston compressors arranged according to the general design contained in the French Patent No. 855,700 is diagrammatically shown by way of indicative but not limiting examples in the drawing appended hereto.

Figure l is a longitudinal sectional view taken on the broken line A-O-B in Fig. 2;

Figure 2 is a top view of the structure of Fig. 1;

Figure 3 is a longitudinal sectional view of a modification;

Figure 4 diagrammatically shows an embodiment of the invention providing means actuating the driving shaft for driving the fluid distribution attachments;

Figure 5 shows a modification of the apparatus of Fig. 4;

Figure 6 is a detail view of a connecting rod constructed according to the invention;

Figure '7 shows an arrangement for imparting a uniform movement to the shaft that actuates the fluid distribution attachments.

The motor or prime mover cylinder l is connected with the compressor cylinder 2 by a brace (not shown) to hold these cylinders in fixed relation to each other. Movable in the motor cylinder are the motor pistons 3, 4 and 5, and in the compressor cylinder the compressor pistons t. I and B.

The left hand and the right hand parts of the figure are vertical sections taken in Fig. 2 at right angles to each other on line A- and 0-13 in order to show more clearly the means connecting between the various pistons.

It will be seen in the right hand portion of Fig. 1 that the driving pistons 3 and are rigidly connected with each other by two rods 9, as seen in Fig. 2, each of which projects through the motor piston 4 and through a packing gland or a labyrinth packing ill carried by the piston 4. Both of said pistons 3 and 5 are also connected with the compressor piston I by rods I l which pro- ,iect through the piston i and through packing glands or labyrinth packings i2 carried by the piston 6.

Conversely, it will be seen in the left portion of Fig. 1 that the driving piston 4 is rigidly connected by two rods It with the compressor piston 0 which in turn is connected by rods 19 with the 4 compressor piston 8. The rods II and I! respectively project through the motor piston i and the compressor piston I and through packing glands or labyrinth packings III and ii carried by pistons 5 and I.

The intake ports l4, l5 and the exhaust ports l4, ii of the compressor cylinder 2 are located close to the plane of symmetry of the reciprocating movement of the corresponding pistons 5 and I on one hand, 1 and I on the other hand. Similarly, the intake ports i6 and i1 and the exhaust ports 18' and ll of the motor cylinder I are located close to the planes of symmetry of the motor pistons I and 4 on one hand, 4 and 5 on the other hand.

The two groups of movable elements, which are constructed so as to have equal weight and which at all times are urged by equal and opposite forces according to the specifications of the already mentioned Patent No. 855,700, are suspended in the usual way through a system of equalizers (not shown) on a suspension shaft It.

It will be appreciated that the machine provides for one driving impulse and one compression stroke for each stroke of the motor or prime mover and that consequently no expedient such as an air cushion or the like is required for returning the movable systems to their dead centres.

Obviously, this invention is independent of the pressures and temperatures of the driving and the compressed fluids.

The embodiment shown in Fig. 3 relates to an arrangement where the motor and the compressor cylinders have the same diameters and are located one directly above and continuous with the other. In this case the suspension shaft I8 is arranged at the upper end of the machine. The number of pistons in this embodiment is limited to five and the unit is very compact.

In the arrangement shown in Fig. 4, BI and 32 are members of the movable systems of a machine provided with suitable free pistons by which the rocking shafts l1 and 3B synchonized by the connecting rod 38' are actuated through the medium of links 33, 34 and levers 35, 36 respectively supported to oscillate on shafts 31 and 38.

According to this feature of the invention, a shaft 3! driving the attachments or the fluid distribution gear is given a rotary motion through the medium of crank 40 and crank pin 42 and rod 4| connected with one arm of lever 36 mounted on shaft 38, this mechanism being elastic as a whole, as will be understood from further description, and shaft 39 possessing a given amount of inertia to enable the crank pin 42 to move past the dead centres. For various reasons attributable to the conditions of operation of free-piston machines, the angle swept over by the shafts 31 and II in their oscillations is not constant. If the mechanism 40- were rigid, strains upon it would result that would be out of proportion with the forces this mechanism must transmit to the attachments or the distribution gear, while the pistons would no longer be free.

The dead centre can also be passed by resorting to the driving torque of an electric motor connected in driving relation to the shaft 39.

The inequalities of the amplitude of the rocking movement may at times be considerable. The elastic character to be conferred to crank 40 and rod 4| then is inconvenient as a result of the consequences on the movement of shaft 39. The

ascasss improvement shown in Fig. allows a remedying of the said inconvenience.

Keyed on shaft 1! in Fig. 5 is a spur wheel 4! meshing with the pinion 44 which is mounted on a common shaft with arm 45 to which is connected rod 46 and crank 41 of rotary shaft 48. The ratio of the gearing 43- is so selected that crank it shall describe an arc of about 180. It will be appreciated that by this contrivance the consequences of the positive or negative differences in the amplitude of the swinging movement of lever 86 with respect to its mean value are lessened considerably.

The rod-and-crank mechanism 40- may be given a yielding character, and the play can be limited by a pair of springs such as cup washers ill (Fig. 6) wedged in a suitable position, e. g. by means of block ii and screw 52.

The speed of the rotary shaft is not strictly a function of that of the movable units, that is, the piston and parts connected thereto. Said speed need not be exactly constant. Where profitable it is possible to convert the same into a constant or substantially constant speed through the medium of a highly flexible coupling contingently combined with a friction coupling.

To this end in Fig. '7 a rotary Shaft 48 represents the shaft the movement of which is not uniform. Through the medium of any suitable friction coupling 53 and of the flexible coupling 54, which can be a simple torsion bar, the shaft 55 is impelled with a practically uniform movement, provided the characteristics of the said contrivanoes and the inertia of the said shaft 55 are suitably selected. The working of this system is obvious.

The attachments or distribution gear referred to as shown in Fig. 4 may comprise a gear 80 fastened on the shaft 39 and meshing with gear 62 fastened on a valve operating cam shaft 83 supported in suitable bearings not shown. when the shaft 39 is driven in the direction of the arrow in Fig. 4 by the connecting rod ll and crank I! the shaft 83 will be rotated in the clockwise direction as shown by the arrow. Fastened on the shaft 63 is a cam 85 engaging a cam follower G1 which may be rigidly fastened to a valve 69 biased upwardly in Fig. 4 by spring Ii. The valve 89 has a portion fitting in sliding relation against the wall 0! the cylinder in which the oppositely moving pistons are shown at the ends of the stroke in which they are adl acent.

Valve 6! controlling port 13 may be the exhaust valve which in the position shown in Fig. 4 has been closed in preparation for the power stroke. A valve controlling a port displaced about the axis of the cylinder from the port It may be operated by a cam of suitable form fastened on the shaft 63 for control of admission oi the fluid pressure medium between the pistons to produce the opposite movement thereof. The cam 65 is of such form as to maintain the valve is closed during the power stroke as the pistons separate. When the pistons reach the opposite ends of respective strokes the cam 65 will have rotated to the position where the follower BI is in contact with the low portion of the cam to permit the spring II to move the valve 69 upwardly to open port II, thereby to provide for the exhaust of the fluid pressure medium from between the pistons in the cylinder as they move toward each other in the reverse strokes thereof. During these exhaust strokes the valve controlling the port I! will be closed by its cam.

The distribution or valve gear driven by the transmission mechanism shown in Fig. 4 is merely diagrammatic and may be varied to suit different constructions of the apparatus of the invention while controlling the admission of the fluid pressure medium between the oppositely moving pistons in the cylinder and the exhaust therefrom in proper time relation to the movement of these pistons in the cylinder.

What we claim as our invention and desire to secure by Letters Patent is:

1. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination with a prime mover cylinder for expansion therein of fluid under pres sure to develop the power to drive the compressor, and a gas compressor cylinder for compression of a gas therein, of a plurality of pistons in each of said cylinders, alternate pistons in each cylinder being connected to move together in their respective cylinders in the same directions of forward and reverse movement, at least two connected pistons in one cylinder being connected to at least one piston in the other cylinder, means for introducing fluid under pressure between adjacent pistons of the prime mover cylinder to drive them in opposite directions in said prime mover cylinder to drive the corresponding pistons of said compressor to which they are connected in opposite directions in said compressor cylinder, and means for confining the gas to be compressed between pistons of said compressor cylinder which are moving toward each other to effect compression of said gas.

2. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1 in which a given piston between two other pistons of one cylinder is connected to two pistons in the other cylinder at either side of a piston therebetween.

3. In a fluid pressure machine having a prime mover and a gas compressor driven bysaid prime mover, the combination as defined in claim 1 in which a given piston between two other pistons of one cylinder is connected to a given piston in the other cylinder between two other pistons of said other cylinder.

4. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1, the number of pistons in each cylinder being odd.

5. In a fluid pressure machine havin a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1, said cylinders each being provided with intake and exhaust ports positioned in the length thereof so as to communicate with the space between said pistons when said pistons are in positions in the reciprocation thereof in which they are adjacent to each other, and valves for said ports for controlling the intake and exhaust of the fluid and gas into and from said cylinders.

6. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1, said cylinders having a common axis and a common bore, one of said pistons being common to both cylinders.

7. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1 in which each cylinder is provided with three pistons, the middle piston of each cylinder being connected to the two outer pistons of the other cylinder to move together therewith.

amazon 8. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1 in which each cylinder is provided with four pistons, whereby the two inner pistons in each cylinder are adapted to operate as a high pressure stage and these two inner pistons are adapted to cooperate with the respective outer pistons of said cylinder to operate as the low pressure stage.

9. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover the combination as defined in claim 1, said cylinders having a common axis and a common bore, the number of pistons in said common bore being odd, one of said pistons being common to both cylinders.

10. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination as defined in claim 1, a rocker shaft, levers carried by said shaft and extending therefrom for reciprocating angular movement of said levers, and links connecting said levers respectively to the alternate groups of connected pistons which respectively 'comprise pistons in the prime mover cylinder connected to pistons in the compressor cylinder.

11. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover the combination as defined in claim 1, a.

reciprocatable member operatively connected to and to reciprocate with the connected groups of pistons which comprise pistons in the prime mover cylinder connected to pistons in the gas compressor cylinder, a rotatable member, means for operatively connecting said reciprocatable member to said rotatable member to produce rotation of said rotatable member upon reciprocating movement of said reciprocatable member produced by movement of said pistons, said rotatable member being operatively connected to said means for introducing fluid under pressure and to said means for confining gas to be compressed to control the driving of said prime mover and the compression of said gas.

12. In a fluid pressure machine having a prime mover and a gas compressor driven by said prime mover, the combination with a prime mover cylinder for expansion therein of fluid under pressure to develop the power to drive the compressor, and a gas compressor cylinder for compression of a gas therein, of a plurality of pistons in each of said cylinders, at least two of said pistons in each cylinder being connected to move together in said cylinder in the same directions of forward and reverse movement and being adapted to move oppositely to at least one other of said pistons of the same cylinder, at least two connected pistons in one cylinder being connected to at least one piston in the other cylinder, means for introducing fluid under pressure between oppositely moving pistons of the prime mover cylinder to drive them in opposite directions in said prime mover cylinder and to drive the corresponding pistons of said compressor to which they are connected in opposite directions in said compressor cylinder, and means for confining the gas to be compressed between the pistons of said compressor cylinder which are moving toward each other to effect compression of said gas.

13. A fluid pressure machine comprising a prime mover cylinder having at least two pistons oppositely reciprocatable therein lengthwise of the axis of said cylinder, a gas compressor operatively connected to said pistons to be driven thereby concomitantly with reciprocating movement of said prime mover pistons to compress gas in said gas compressor, a rocking shaft, means operatively connecting said pistons to said rocking shaft so as to provide concomitantly with said movement of said pistons in opposite directions in said cylinder movement of said rocking shaft in the respective directions of said rocking movement thereof, a unidirectionally rotatable shaft, means operatively connecting said rocking shaft to said rotatable shaft adapted to set said rotatable shaft in rotation concomitantly with rocking movement of said rocking shaft and providing for differential movement of said rocking shaft and said rotatable shaft relative to each other during said concomitantly rocking and rotational movements thereof. means for controlling delivery of a fluid under pressure to said prime mover cylinder periodically and concomitantly with the movement of the pistons therein for effecting said opposite reciprocating movement of said pistons, and means operatively connecting said unldirectionally rotatable shaft to said fluid delivery controlling means for operating said fluid controlling means concomitantly with the reciprocating movement of said pistons.

14. A fluid pressure machine as defined in claim 13 in which said means operatively connecting said rocking shaft to said rotary shaft comprises means providing elastic yielding movement of said connecting means relative to said rotary shaft to compensate for variations in the relative movements of said shafts.

15. A fluid pressure machine as defined in claim 13 in which said means operatively connecting said rocking shaft to said rotary shaft comprises an arm carried by said rocking shaft, a crank rotating with said rotary shaft, and a connecting rod connecting said arm to said crank.

16. A fluid pressure machine as defined in claim 13 in which said means operatively connecting said rocking shaft to said rotary shaft comprises an arm carried by said rocking shaft, a crank rotating with said rotary shaft, a connecting rod connecting said arm to said crank, and means cooperating with said crank for providing substantial inertia to carry said connecting rod past dead center.

17. In a fluid pressure machine having a prime mover and a gas compressor driven in said prime mover, the combination as defined in claim 1 in which the mass of one set of connected pistons and their connections is substantially equal to the mass of the other set of connected pistons and their connections.

18. A fluid pressure machine comprising a prime mover cylinder, a pair of pistons in said cylinder oppositely reciprocatable therein lengthwise of the axis of said cylinder, means for controlling delivery of fluid under pressure into said cylinder periodically and concomitantly with movement of the pistons therein to act on said pistons to drive them in opposite directions to develop power under the pressure of said fluid introduced into said cylinder, a mechanical power absorbing means operatively connected to said prime mover pistons to be driven thereby concomitantly with said opposite reciprocating movement of said pistons, a rocking shaft, means operatively connecting said pistons to said rocking shaft to effect rocking movement of said rocking shaft concomitantly with said reciprocating movement of said pistons in opposite directions, a unidirectlonally rotatable shaft, means operatively connecting said rocking shaft to said rotatable shaft adapted to set said rotatable shaft 9 in rotation concomitantly with rocking movement of said rocking shaft, and means operativeiy connecting said unidirectionaiiy rotatable shaft to said fluid delivery controlling means for operating said fluid delivery controliing means concomitantly with reciprocating movement of said pistons.

ERNEST MERCER.

MARCEL EHLINGER.

REFERENCES CITED The following references are of record in the tile of this patent:

10 ourran s'ra'rns m'mn'rs Number Number ll 040,720 770.023

Name Date smith Nov. 20. 1888 Spencer Aug. 1'1. 1897 Bchiflbauer Am. 25. 1905 Wolfe Dec. 8, 1931 Bard Aug. 2, 1982 Pescara Mar. 30, 1937 Brun Nov. 2. 1987 Steiner May 8, 193B Jorgensen May 11, 1943 FOREIGN PATENTS Country Date Germany Nov. 1, 1038 France June 18, 1934 

